The invention relates to a process for the preparation of a bisphosphine dioxide with formula ##STR1## in which R.sub.1, R.sub.2, R.sub.3 and R.sub.4, being the same or different, represent substituted or unsubstituted alkyl-, aryl-, alkaryl- or aralkyl groups or an alkylene group is formed by R.sub.1 and R.sub.2 and/or R.sub.3 and R.sub.4 respectively, R.sub.5 represents H, R.sub.6 represents H or a substituted or unsubstituted alkyl-, aryl-, alkaryl- or aralkyl group, or R.sub.5 and R.sub.6 form an alkylene group, and to bisphosphine dioxides obtained by this process.
Bisphosphines are widely employed as bidentate ligands in transition metal, in particular Group VIII noble metal (e.g. rhodium), catalyzed reactions such as hydrogenation, hydrosilylation and hydrocarbonylation. Owing to the structure of these ligands various electronic or steric influences can be exerted in the close environment of the chelated metal centre. Accordingly, the selectivity of the catalysts strongly depends on the structure of the bisphosphines used as ligands, which structure may e.g. give rise to asymmetric hydrogenation. In this way the hydrogenation of unsaturated comounds to form saturated compounds having optical activity may be achieved. As an example the hydrogenation of substituted acrylic acids and esters to form stereoisomers of amino acids (e.g. phenylalanine, hydroxyphenylalanine, .beta.-indolylalanine and dihydroxyphenylanaline) may be mentioned.
Bisphosphines can be easily prepared from bisphosphine dioxides by well known techniques such as reduction with a mixture of chlorosilanes and trialkylamines, or with aluminum hydride.
Methods for the preparation of bisphosphine dioxides are known, but they are complicated and do not give satisfying yields.
The invention provides an attractive method for the preparation of bisphosphine dioxides in high yields, by reaction of oxiranes with secondary phosphine oxides.